Preparation Of Carbonate Nanofluids And Their Thermal Properties

Exploring and utilizing clean and renewable energy can meet the requirements of current energy and environmental development.Solar thermal power generation is an important way for large-scale application of renewable energy.In order to solve the problem of intermittent and stability of solar energy and improve the operating efficiency of solar thermal power generation systems,it needs a heat transfer and heat storage medium with good thermal properties,low cost and environmental friendliness.Due to its wide operating temperature,low steam pressure,low cost and high temperature stability,molten salts are widely used in solar thermal power generation,power grid system,industrial waste heat utilization,etc.But its specific heat capacity and thermal conductivity is lower than traditional heat storage materials.In this paper,nanofluids were prepared based on carbonates with a working temperature higher than800?.The preparation methods and conditions for thermal properties enhancement of nanofluids were investigated.The nanofluids of ternary carbonate K₂CO₃-Li₂CO₃-Na₂CO₃?4:4:2,mass ratio?with SiO₂,Al₂O₃ and carbon nanotubes?CNT?nanoparticles were prepared.We investigated the effects of evaporation methods?electrothermal drier and hot plate?,nanoparticle concentration?0.25,0.5,1.0,1.5,2.0wt%?,evaporation temperature?100,120,140,160,180,200,220,240??and surfactants?sodium dodecylbenzene sulfonate,sodium lauryl sulfate,gum arabic?in the two-step solution method and stirring time?15,30,60 min?and stirring rate?500,750,1000 rpm?in the high temperature melting method on the thermal properties of the nanofluids.The results show that:?1?For the nanofluids with SiO₂ nanoparticles prepared by electrothermal drier and hot plate at evaporation temperature of 180°C in a two-step solution method,the enhancement of specific heat capacity is 129.3%and 33.5%,respectively.The reason is mainly related to the change of the composition ratio of sample caused by different evaporation methods,especially the ratio of Li₂CO₃;?2?The optimum concentration of SiO₂ and Al₂O₃ nanoparticles in sample is 1.0wt%,but the SiO₂ nanoparticles are the most effective addition on enhancing the specific heat capacity and thermal conductivity of ternary carbonate;?3?The enhancement of specific heat capacity of nanofluids with CNT is 26.3%.The sodium lauryl sulfate as a surfactant can improve the dispersion of CNT in nanofluids at evaporation temperature of 140?,and the corresponding enhancement of specific heat capacity and thermal conductivity is 77.6%and 149.2%,respectively;?4?For the preparation of SiO₂-ternary carbonate nanofluids by high temperature melting method,the specific heat capacity and thermal conductivity can reach to 38.5%and 50.0%,respectively,at the optimum stirring rate of 750 rpm for 30 min.The sample exhibits a good thermal stability after undergoing high thermostatic and large temperature difference thermal shock experiments;?5?Based on the characterization of XRD,it can be seen that no new substances were formed in the sample after the addition of nanoparticles.From SEM images,it can be found the formation of special nanostructures with a large surface area,which can form a heat channel for heat transfer and improve the specific heat capacity of sample.Suitable preparation methods and conditions have significant impact on dispersing the nanoparticles and promote the formation of nanostructures.